Boring bit and method of manufacture

ABSTRACT

A boring bit has a shank, a head and teeth distributed around the head. The teeth have a root embedded within the head&#39;s core body, a tip extending out of the head, and a narrowing region between the root and the tip. More than approximately two-thirds of the tooth length is embedded in the core body, including a portion of the narrowing region. Stabilizing rods are welded to the tips of the teeth to form a temporary connection, and the core body is formed from a molten metal poured into a cavity of a cast mold. The rods are inserted into indentations in the cast to hold the teeth in place, and the molten metal heats the teeth and weld to substantially loosen the temporary connection. As the molten metal cools, it solidifies around the teeth and secures the root and narrowing region of the teeth within the core body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application No. 61/786,516 filed on Mar. 15, 2013 which is hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

APPENDIX

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to boring bits for the drilling heads of directional boring machines, and more particularly to the design and method of manufacture of the teeth used in the boring bits.

2. Related Art

Boring bits are used in a number of directional boring machines. Generally, directional boring or horizontal directional drilling (HDD) is a steerable trenchless method of installing pipes, conduits and cables along an underground route that is formed from a drilling rig at one end of the route. There are different types of heads used in the pilot-hole process, and they depend on the geological material.

In most boring operations, drilling fluid is used to cool the boring head and to lubricate and soften the spoils. The fluid is usually pumped and delivered to the end of the boring head by means of some conduit through the drill string, and the fluid exits the boring head through the fluid nozzle. The pumped fluid is ported around the cavity housing the electronic components, thereby cooling it. In most boring head assemblies, the fluid is not typically directed ahead of the boring bit to the front most part of the boring operation. Instead, the fluid may be directed toward the head of the boring bit, but the fluid is actually deposited on the shank of the boring bit, and it is not passed through the head of the boring bit or through the head of any other earth drilling or cutting tool that may be attached to the front of the boring head assembly. In the few boring head assemblies in which the fluid is directed ahead of the boring bit, the fluid is typically channeled into multiple conduits to help with the boring. However, the fluid exits at multiple conduits at different angles which vary from the axis of the drill stem and beacon housing unit so the fluid does not provide any significant assistance in the steering of the head.

In the manufacture of the boring bits, the body of the bit, including the head portion, may be formed from any known casting process. However, the carbide teeth are not typically formed in situ with the body of the bit during the casting process for current boring bits. Instead, the manufacturing processes for current boring bits require one or more post-casting steps to secure the carbide teeth into the body. For example, one post-casting step could be to press punch the teeth into the body of the bit so that there is formed an interference fit between the teeth and the body. Other methods to attach the teeth to the body include brazing the teeth onto the body, screwing or threading the teeth into the body, or spot welding the teeth to the body. For those manufacturing methods which incorporate teeth into the cast while molten metal is poured into the cast's cavities, these methods do not provide a good way to temporarily hold the teeth to indentations in the cast while the molten metal fills around the teeth and loosen the hold on the teeth as the metal solidifies.

SUMMARY OF THE INVENTION

In one aspect of the invention, a boring bit for a directional drilling machine has a shank, a head and a plurality of teeth distributed around the head. Each of the teeth has a root embedded within the head's core body and a tip extending out of the head away from the head's peripheral surface. The teeth also have a narrowing region between the root and the tip. More than approximately two-thirds of the tooth length is embedded in the core body, including a portion of the narrowing region.

In another aspect of the invention, stabilizing rods are welded to the tips of the teeth to form a temporary connection, and the core body is formed from a molten metal poured into a cavity of a cast mold. The stabilizing rods are inserted into indentations in the cast to hold the teeth in place, and the molten metal heats the teeth and the weld and substantially loosens the temporary connection. As the molten metal cools, it solidifies around the teeth and secures the root and narrowing region of the teeth within the core body.

In yet another aspect of the invention, the peripheral surface of the head has a top surface, a bottom surface, a side surface between said top surface and said bottom surface in which the teeth are embedded, and an angled surface between the shank and the top surface. A single passageway extends through the core body from an entrance in the angled surface to an exit in the bottom surface. The single passageway has a planform centerline aligned with a longitudinal axis of the drill stem.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings. The drawings constitute a part of this specification and include exemplary embodiments of the invention, which may be embodied in various forms. It is to be understood that in some instances, various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention; therefore the drawings are not necessarily to scale. In addition, in the embodiments depicted herein, like reference numerals in the various drawings refer to identical or near identical structural elements.

FIG. 1A is an isometric view of the boring bit according to the present invention.

FIG. 1B is a plan view of the boring bit shown in FIG. 1A.

FIG. 1C is a cross-sectional view of the boring bit through the plane AA as shown in FIG. 1B.

FIG. 1D is a detail view of a tooth in the boring bit as shown in FIG. 1C.

FIG. 1E is an isometric view of a tooth.

FIG. 2 is a side view of the boring bit operating underground.

FIG. 3A is a cross-sectional view of a cast mold with embedded teeth and stabilizing rods.

FIG. 3B is an isometric cutaway view of a tooth and stabilizing rod embedded in a cast mold receiving molten metal.

FIGS. 4A and 4B are cross-sectional views of teeth with stabilizing rods and optional cast arrangements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the inventive boring bit 10 for a horizontal directional drilling machine is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Generally, as shown in FIG. 1A, the boring bit 10 of the present invention has a body with a head portion 12 connected to a shank portion 14, and teeth 16 are radially distributed around the periphery of the head portion. Preferably, the head has an upper row of teeth 16 a, a lower row of teeth 16 b and a middle row of teeth 16 c which are angled relative to each other. In particular, the upper and lower rows have diverging teeth axes 88 a, 88 b relative to a plane 90 through the center of the head, and the axes of the teeth in the middle row are aligned with the head's center plane. The head has a top surface 62 proximate to the upper row, a bottom surface 64 proximate to the lower row, and angled surface 66 between the shank 14 and the top surface 62. Also, as explained in further detail below, a passageway 68 extends through the head.

FIG. 1B is a plan view of the boring bit 10 shown in FIG. 1A, and FIG. 1C is a cross-sectional view of the boring bit 10 through the plane AA as shown in FIG. 1B. As shown in FIGS. 1C and 1D, each of the teeth has a root 18 embedded within the head 14 and a tip 20 extending out and away from the head's outer surface. The teeth have a narrowing region 22 between the root and the tip, and the length 24 of the tooth is measured from the root's bottom 26 to the top of the tip 28. The narrowing region 22 has a decreasing width 30 from the root width 32 to the tip. According to one aspect of the invention, the head portion has a core body 34 that is formed from a molten metal 54 that solidifies around the teeth 16 and extends to a peripheral surface 36, and more than approximately two-thirds (⅔) of the tooth length 24 is embedded in the core body 34. It is preferable that at least a portion of the core body 34 covers a portion of the narrowing region 22 of the teeth which helps to hold the teeth within the head 14.

The head 14 also has a passageway 68 that extends through the core body 34 from one location proximate to the shank portion 12 to another location at the periphery of the head 14 distal from the shank portion. The proximate location is on one side of the head and the distal location is on a second side of the head. As particularly shown in FIG. 1C, a single passageway 68 extends through the boring bit's core body 34 from an entrance 68 a in the angled surface 66 to an exit 68 b in the bottom surface 64. The entrance 68 a to the passageway 68 has a countersunk hole 70 with an outer diameter approximately twice the inner diameter of the passageway. The exit of the passageway in the bottom surface is located at a substantially planar surface 78 and is preferably not located between a pair of teeth in the head.

As is also shown in FIGS. 1B and 1C, the boring bit 10 is connected to a drill stem 72 with a nozzle 74 extending to the passageway's entrance 68 a. According to another aspect of the present invention, the single passageway 68 has a planform centerline 68 c which is aligned with the drill stem's longitudinal axis 76. In connecting a mounting surface 60 a of the boring bit 10 to the drill stem 72 and beacon housing, the standard water jet nozzle is removed from the beacon housing and is replaced with the water jet extension nozzle 74 according to the present invention. The extension nozzle 74 preferably has a diameter approximately equal to the inner diameter of the passageway.

The fluid that flows through the drill stem can be controlled by the operator and as shown in FIG. 2, the passageway 68 directs the fluid 100 ahead of the boring bit 10 to the ground 110 being bored. The rate of the fluid flow is controllable up to its maximum rate. In one embodiment, the maximum flow rate is eighty gallons per minute (80 gpm). By varying the flow rate through the passageway, the operator can vary the directional force 120 on the head 14 which assists the operator in steering the boring bit 10 through the ground 110. As the force 120 is increased, the turning ability of the boring bit is increased so that a greater force produces a greater degree of turn. Accordingly, the directed jet 105 helps to loosen the earth in the same region of the ground 110 where the boring bit is working to prepare a pilot-hole 115 and is also helpful in steering the boring bit through the ground around obstacles, such as buried cables, pipes and other fixed structures in the ground.

As particularly shown in FIG. 1C, the head 14 is angled relative to the shank 12 by approximately ten degrees (10°). This tilt angle combined with the different angles of the teeth axes in the three rows of teeth helps to center the head 14 relative to the longitudinal axis 76 of the drill stem 72. By centering the head 14, the forward-facing teeth in the head can produce a pilot hole through which the boring bit 10, drill stem 72 and beacon housing follow.

Several aspects of the teeth 16 are particularly shown in FIGS. 1D and 1E. According to the embodiments shown in the drawings, the root has a substantially cylindrical surface 58 with a pair of notches 60 in the cylindrical surface in a manner that the core body 34 is in fixed contact with the cylindrical surface and with the notch. It will be appreciated that although the cylinder is shown as having a circular cross-sectional shape, other shapes may also be used. Accordingly, the cylinder shape can be any type of design. Additionally, the shape of the tip 20 of the teeth, or the button, can be changed to create different cutting reactions in different rock and soil formations and ground conditions. The fixed contact between the solidified molten core and both the cylindrical surface and the notch provide a positive lock between each one of the teeth and the head portion. In particular, the solidified molten core projects from the cylindrical surface into the notch to form the positive lock between the teeth and the head.

The manufacturing process to produce the boring bit 10 is described in detail below with reference to FIGS. 3A and 3B. During the manufacturing process, the tip 20 of each of the teeth 16 is embedded in a cast mold 42 and the root 18 of each of the teeth extends out from the cast into the cast's internal cavity 44. The teeth are preferably formed from tungsten carbide buttons which may be a tungsten carbide steel alloy, and as indicated above, the head portion is formed from a molten metal 54 poured into the cast, such as a hardened, wear-resistant steel. Accordingly, the teeth are formed from a material having a melting point that is at least 1,000° F. greater than the molten metal. In producing the boring bit, stabilizing rods 40 are preferably brazed or welded onto the tip 20 of the teeth 16 so that the rods extend from the respective tip of the teeth further into the cast mold 42 and secure the teeth in their respective positions and orientations within the cast. As described below, the weld 50 is a temporary connection 52 between the rods 40 and the teeth 16 that releasably holds the teeth to the cast 42.

The particular casting process is described with reference to a sand cast 42, but it will be appreciated that other cast molds and casting techniques could also be used to create the boring bit 10 according to the present invention, such as investment casting process (“lost wax” cast mold) and other releasable connections 52 between the teeth and the cast may be possible, such as a heat-resistant epoxy temporarily connecting the cone section of the teeth and the cast. Accordingly, although the preferred embodiment of the invention uses stabilizing rods 40 welded to the teeth to hold the teeth in place in the sand cast 42, other releasable connections between the teeth and cast can be within the scope of the several aspects of the present invention.

A sand cast 42 is preferably formed with a cavity 44 having an inner surface 46 in the shape of the shank 12 and head 14. There are indentations 48 in the inner surface where the tips 20 of the teeth 16 are inserted into and releasably held within the sand cast 42. The teeth are radially distributed around the head in the rows described above, and additional teeth can be embedded in the sides 60 b of the shank section. A root of each of the teeth extends outwardly from the sand cast into an interior space of the cavity corresponding with the head of the boring bit with a plurality of interstitial spaces between the teeth at their roots. A molten metal is poured into the shank section and head section of the sand cast and fills the interior space and the interstitial spaces between the teeth.

As explained above, it is also preferable to braze the rods onto the tips of the teeth. The rods are inserted into the sand cast which is then hardened with the teeth and the rods in situ. When the molten metal is poured into the sand cast, it heats the teeth and loosens the brazing between said rods and the teeth. The temporary or otherwise releasable connection 52 is generally shown in FIGS. 4A and 4B. After the molten metal is poured, the casted boring bit is allowed to cool so that the molten metal forms a solid body in which the shank portion is preferably formed with the head portion in an integral monolithic bit with the teeth embedded at the root. The sand cast is then broken away from the solid body, and the loosened rods remain in the sand cast. A finished mounting surface 60 a is machined on the side of the shank that is fastened to the drill stem 72; the boring bit's surface can be ground clean and the pour stacks removed. The mounting holes 80 are drilled through the shank and the passageway 68 is drilled in the head 14 with the countersink 70 at the entrance to receive the nozzle 74 for the water jet.

It will also be appreciated that a mold pattern is prepared for the cast. The mold pattern includes recesses that can hold tooth blanks to form the indentations 48 in the inner surface 46 of the cast 42. Molding sand is packed into the mold pattern, and then the mold pattern and the tooth blanks are removed from the packed molding sand. When tooth blanks are used, they are removed from the packed molding sand which leaves a hollow at the periphery of the sand cast. The tips of the teeth are inserted into the hollow as the brazed stabilizing rods are pushed into the packed molding sand. Alternatively, the recesses can hold the carbide teeth with the stabilizing rods already welded to the tips of the teeth so that when the sand is packed into the mold pattern the teeth are already in place.

Accordingly, the present invention generally uses the sand cast mold method of pouring molten steel in to a cavity. The brazed rod is used to suspend the tungsten carbide buttons in a secured position within the sand cast while the molten steel is poured. To braze the rod to the tip of a tooth, the tungsten carbide tooth or button is heated to about 1100 degrees. A threaded carbon steel rod 20 is then brazed onto the end close to center of the tungsten carbide button 16. The rod is preferably long enough, about 12″ or so, to avoid burning the welder. Once the brazing weld is completed, the rod is cut down to about ¾″ long which provides a length that is strong enough to hold in the sand cast mold. Generally, the cut rod's length 56 is longer than the combined length of the root 24 a and the narrowing region portion 24 b which extends into the cavity 44. The length of the tooth's tip portion 24 c that is inserted into the indentation 48 in the cast is less than approximately one third (⅓) the overall tooth length 24.

The sand cast mold can be chemically treated to harden the sand. The sand adheres well to the threaded part of the rod 40 and holds it in place until the molten steel is poured and then solidifies as it cools. As described above, the tungsten carbide teeth have an indent in their roots, preferably more than one indent in each root. The depth of the indent is about 0.005″ and the length is about ¼″ which allows the molten steel to fill in the notch and permanently prevent the teeth from coming loose from the boring bit. Accordingly, the notch provides a positive lock to hold the tungsten carbide teeth in place within the molten metal that solidifies around the teeth.

There are several techniques used for manufacturing the notches in the teeth. The notches can be formed by grinding the tungsten carbide teeth, such as with a green carbide grinding wheel. A carbide grade wheel is used to cut or grind away material (carbide) normally used to sharpen carbide cutters used in cutting steel. Alternatively, the notch or other indention can be cast or otherwise formed or machined in the tooth.

The melting point of the tungsten carbide is over 5,000° F. (approximately 5,200° F.) whereas the melting point of the steel is under 3,000° F. (approximately 2,500° F.-2,800° F.). Accordingly, the tungsten carbide teeth remain solid as the molten steel is poured into the cast. The tungsten carbide teeth conduct the heat to the welded brazing material at the tip of the teeth, the brass heats up and the weld is loosened, releasing the tungsten carbide teeth to the steel as it solidifies around the roots and allowing the rods to remain in the cast where they are embedded. Similarly, heat may reduce the strength of an epoxy temporarily fixing teeth in the indentations.

As shown in FIGS. 4A and 4B, the tip portion of the teeth that extends out from the periphery of the boring bit can be changed by the depth 82 of the indentations in the cast as well as the shape 84 of the cast in the local region 86 around the teeth 16. For example, the depth of the indentations in FIG. 4A and the flat shape 84 a of the cast region 86 surrounding the teeth 16 result in less than approximately one-third of the length of the teeth projecting out from the head's peripheral surface 36. In comparison, the depth of the indentations in FIG. 4B and the faceted shape 84 b of the cast region 86 surrounding the teeth 16 result in less than one fifth (⅕) of the length of the teeth projecting out from the head's peripheral surface 36. The faceted cut-away of the case in FIG. 4B results in a local buildup of metal around this region of the tip. Even without this faceted cut-away in FIG. 4B, it is evident that less than one quarter (¼) of the tooth's length is inserted into the indentation so less than one quarter (¼) of the length of the tooth would project from the peripheral surface. In the examples of FIG. 1, less than approximately one third (⅓) of the tooth 24 c is inserted in the indentation resulting in more than approximately two thirds (⅔) of the tooth 24 a, 24 b being embedded in the core 34.

The embodiments were chosen and described to explain the principles of the invention and its practical application to persons who are skilled in the art. Modifications could be made to the exemplary embodiments, as described above with reference to the corresponding illustrations, without departing from the scope of the invention. All matter contained in the foregoing description and shown in the accompanying drawings is illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents. 

What is claimed is:
 1. A boring bit, comprising: a shank portion; a head portion connected to said shank portion, said head portion having a core body and a peripheral surface; and a plurality of teeth distributed around said head portion, wherein each of said teeth has a root embedded within said core body, a tip extending out of said head portion away from said peripheral surface, a narrowing region between said root and said tip and a tooth length from a bottom of said root to a top of said tip, wherein said narrowing region has a decreasing width from a root width to said tip, wherein more than approximately two-thirds of said tooth length is embedded in said core body of said head portion, wherein said core body of said head portion covers a portion of said narrowing region.
 2. The boring bit of claim 1, further comprising a plurality of stabilizing rods, wherein each of said teeth has one of said stabilizing rods releasably connected to said tip.
 3. The boring bit of claim 2, further comprising a cast mold, wherein said cast mold forms a cavity and comprises an inner surface in contact with said peripheral surface and further comprises a plurality of indentations in which each tip of said teeth are embedded, wherein said stabilizing rods are encapsulated in said cast mold at said indentations and wherein said root and a portion of said narrowing region of said teeth extend into said cavity more than approximately two-thirds of said tooth length.
 4. The boring bit of claim 3, further comprising a weld forming a temporary connection between each one of said stabilizing rods and said tip of said teeth, wherein said core body is formed from a molten metal poured into said cavity, wherein said molten metal heats said teeth and said weld and substantially loosens said temporary connection while said molten metal cools and secures said root and said narrowing region of said teeth within said core body as said molten metal solidifies around said teeth.
 5. The boring bit of claim 4, wherein said teeth are formed from a carbide material having a first melting point at least 1,000° F. greater than said molten metal and wherein said weld is formed from a brazing material having a second melting point less than said first melting point by more than 1,000° F.
 6. The boring bit of claim 3, wherein said stabilizing rods have a rod length and wherein said rod length is greater than a length of said root and said portion of said narrowing region extending into said cavity.
 7. The boring bit of claim 1, further comprising a cast mold, wherein said cast mold forms a cavity and comprises an inner surface in contact with said peripheral surface and further comprises a plurality of indentations, wherein each of said indentations is comprised of a releasable connection with a corresponding one of said tip of said teeth.
 8. The boring bit of claim 7, wherein said core body is formed from a molten metal poured into said cavity, wherein said molten metal substantially frees said releasable connection between each one of said indentations and said tip of said teeth.
 9. The boring bit of claim 8, wherein said releasable connection is comprised of a stabilizing rod welded to said tip.
 10. The boring bit of claim 1, wherein said shank further comprises a mounting face, a pair of sides and a set of teeth embedded into said sides, wherein said root is comprised of a substantially cylindrical surface and a notch in said cylindrical surface, wherein said core body of said head portion is in fixed contact with said cylindrical surface and with said notch.
 11. The boring bit of claim 1, wherein said head portion further comprises an upper row of teeth, a lower row of teeth and a middle row of teeth, a top surface proximate to said upper row of teeth and a bottom surface proximate to said lower row of teeth, an angled surface between said shank and said top surface, a single passageway extending through said core body from an entrance in said angled surface to an exit in said bottom surface.
 12. The boring bit of claim 11, wherein said single passageway at said entrance is further comprised of a countersunk hole having an outer diameter approximately twice an inner diameter of said passageway, wherein said exit in said bottom surface is located at a substantially planar surface and is not located between a pair of said teeth in said head.
 13. The boring bit of claim 12, further comprising a drill stem with a nozzle extending to said passageway, wherein said drill stem has a longitudinal axis, and wherein said single passageway has a planform centerline aligned with said longitudinal axis.
 14. A boring bit for a horizontal directional drilling machine having a drill stem with a longitudinal axis and a nozzle, comprising: a shank portion comprising a mounting face, a back face, a pair of sides between said mounting face and said back face, and a plurality of mounting holes; a head portion connected to said shank portion, said head portion having a core body and a peripheral surface, wherein said peripheral surface has a top surface, a bottom surface, at least one side surface between said top surface and said bottom surface, and an angled surface between said shank and said top surface, a single passageway extending through said core body from an entrance in said angled surface to an exit in said bottom surface, wherein said single passageway has a planform centerline aligned with the longitudinal axis; and a plurality of teeth distributed around said head portion, wherein each of said teeth has a root embedded within said core body, a tip extending out of said head portion away from said peripheral surface, a narrowing region between said root and said tip and a tooth length from a bottom of said root to a top of said tip, wherein said narrowing region has a decreasing width from a root width to said tip, wherein more than approximately two-thirds of said tooth length is embedded in said core body of said head portion, wherein said core body of said head portion covers a portion of said narrowing region.
 15. The boring bit of claim 14, wherein said wherein said root is comprised of a substantially cylindrical surface and a notch in said cylindrical surface, wherein said core body of said head portion is in fixed contact with said cylindrical surface and with said notch and provides a positive lock between each one of said teeth and said head portion with said core body projecting from said cylindrical surface into said indentation.
 16. The boring bit of claim 14, further comprising a plurality of stabilizing rods, a cast mold and a weld forming a temporary connection between each one of said stabilizing rods and said tip of said teeth, wherein each of said teeth has one of said stabilizing rods releasably connected to said tip, wherein said cast mold forms a cavity and comprises an inner surface in contact with said peripheral surface and further comprises a plurality of indentations in which each tip of said teeth are embedded, wherein said stabilizing rods are encapsulated in said cast mold at said indentations, wherein said root and a portion of said narrowing region of said teeth extend into said cavity more than approximately two-thirds of said tooth length, wherein said core body is formed from a molten metal poured into said cavity, wherein said molten metal heats said teeth and said weld and substantially loosens said temporary connection while said molten metal cools and secures said root and said narrowing region of said teeth within said core body as said molten metal solidifies around said teeth.
 17. A method for manufacturing a boring bit, comprising the steps of: forming a cast having a cavity for a head portion with an inner surface and a plurality of indentations in said inner surface; embedding a plurality of teeth in said indentations of said cast, wherein a tip of each of said teeth contacts said indentations and wherein a root of each of said teeth extends outwardly from said cast into said cavity of said head portion, said tip being less than one half of a tooth length and said root extending more than one half of said tooth length into said cavity; creating a temporary connection between said tip of each of said teeth and said cast at said indentations; pouring a molten metal into said cavity of said cast, said molten metal surrounding said root of each of said teeth and filling said cavity to said inner surface, wherein said molten metal heats said teeth and loosens said temporary connection between said tip and said cast.
 18. The method of claim 17, wherein said step of creating said temporary connection is further comprised of the steps of welding a plurality of stabilizing rods onto said teeth at said tip, inserting said stabilizing rods into said cast at said indentations and hardening said cast with said teeth and said rods in situ.
 19. The method of claim 18, further comprising the step of cooling said molten metal to solidify into a core body supporting each of said teeth at said root as said temporary connection between said tip of said teeth and said cast is loosened, breaking off said cast from a solidified core body with said stabilizing rods remaining in said cast, and drilling a passageway in said head portion through said solidified core body.
 20. The method of claim 19, further comprising the step of preparing a mold pattern for said cast, wherein said mold pattern includes a plurality of recesses for at least one of said teeth and a plurality of tooth blanks. 